Process of deep etching of zinc by electrolysis.



UNITED srArEs imer orrron.

OF WAINZ, GERMANY. 4 a

, eno ct-zss or- DEEP sToHme F zmc BY ELECTROLYSIS.

Specification of Letters Patent. Applicatich filed May 26; 1904. SerialNo. 209,977.

. Patented March 20, 1906.

To-aLZ-Z whom it may concern:

Be it known that we, Or'ro CARL STRECKER,

v residing at the city-of Darmstadt, and HANS and useful Improvements inProcesses for HERMANN STREoKnR, residing at the city of Mainz, GermanEmpire, doctors of hilosoby and subjects [of the Grandj= uke of lIesse-Darmstadt, have invented certain new the Deep Etching of Zinc byElectrolysis and we do hereby declare that the following is a full,clear, and exact description of the invention:

pure zinc, was used. T

This invention relates to processes for the deep etchingof Zinc byelectrol sisfor the SP 'P ose of rmting impressionst erefrom. In theeectrol tic-production of deeplyetched zincograp s and reliefetchingsfor litho aphic metal printing there could hith erto e obtained aserviceable-etched ground (especially deeply-etched parts) only intheeventthat a perfectly plure metal, such as e impurities-such aslead,'iron,- andcarbon occurring even in thebest commercial brands ofthe article bring about an irregular solution of the zinc,

j andthere is obtained a mu h unequally-bitten etched ground, which taes the color. and

1 is printedoff. The limits of the relative proplate, there appearsunder it a smooth etched current strength effects thera orti ons of zincand the principal impurities ound in commercial'zinc' are 94.4 71 Z1110and- 99.378 zinc, 2.393 lead and 0.503 le ad 0.136 iron and 0.041 iron.(See Graham. Otto,

Manual "of Chemistry, Vol. 1-11, page 755.) According to the presentinvention, however,

a good smooth etched ground is obtainable even with 3 the use of impurezinc, provided, that during the etching ofthefzinc plate employed as anocurrentstrength'of at east two amperes torieach square decimeter ofmetallic one si'ded ployed. The m twelve amperes.

current density is The application of thishigh id and smooth solutionofthe zinc from the zinc. late',,w'hich "plat'e'must be regarded a'san aloy o i'rlead with zinc containing carbon. Moreover, the

impurities, whichare either the insoluble carbon or the hardly-solublelead, remain behind as a'soft coating loosely adherentto the plate;

If this coating be then removed from the ground. If, on the other hand,the work is effected by means of a low current strength,

later.

gan'ode surface be em OTTOCARLSTRECKER, or DAR'MSTADT, AND HANS HERMANNsTREoKER,

machine even large zinc plates may-be etched according tothe newinvention.v

The coating ofimpurities formed in consequence of the action of thecurrent upon the etched plate adheres 'sufficiently firmly that it canbe taken, together with the plate, out

of the bath, whereby the bath is kept free 7 If zinc ace- 'tate or zincformiate be made use of, the.

from muddiness and impurities.

bath is, kept clean in the above-described manner and at the same timethe cathode is so proportioned that it also corresponds to a higcurrentstrength, then the operation on a permanent scale is renderedpossible. With the use of a high current intensity also at the cathodeof at least two amperes'per square decimeter of metallic one-sidecathode surface the zinc at the cathode is electrolytically separated inacontinuous firmly-adherent layer. In this manner there are avoided,-

first, short circuits through conducting metal brid es between theplates, and, secondly, the ath may be maintained constant in itscomposition even in continuous working.

In place of acetate or formiate ofzinc other zinc-salts might be usedfor the bath in so far as they possess the same properties as the zincacetate and zinc formiatenamely, thatthe precipitate electrolyticallyzinc at the cat ode in a continuous layer under high two amperes persquare decimeter of metallic one-side cathode surface. For the operationof continuous working attention mustbe given consequently, on the onehand, to the 'gh current strength at'the cathode, and on the other hand,also and at thesametime a suitable zinc-salt must be employed. With alower current strength at the anode the sediment or skin of impuritiesremaining thereon falls into the bath and causes dis- 95 currentstrength at the cathode of at least fei'e with the printin or else intoa soluble turbances of the working through the sedi- Inent. Moreover, atthe cathode disturbances of the continued working may arise by the zincseparating in the form of a sponge or tree. Thisinconvenience isobviated by having a high current strength at the cathode also and atthe same time making use of such zinc-salts for the bath as willseparate the zinc at the cathode in continuous form under high currentstrength. Such zinc-sal ts therefore should not be used which would tendto separate the zinc at the cathode with the fonmation of spongy ortree-shaped formations even at high current strength.

The new process is referably carried out as follows: The Zinc p ateprovided with the greasy drawing or print is rolled with color,gurnr'ned, and washed with washing tincture or turpentine over the drygum. The drawing is then protected by a coating of greasy asphaltsolution or the like, dried, and washed. The plate thus prepared is thensuspended as anode in a bath, which consists of about ten per cent. ofzinc-acetate solution and has a zinc cathode. Hereupon an electriccurrent is sent through the bath, which possesses a current strength ofat least two ampere's per square decimeter of metallic one-sided anodesurface. Obviously several baths may be arranged in series. The platesmay be suspended vertically, or they may he placed horizontally in thebaths, because neither spongy zinc nor hydrogen are produced and theadherence of the impurities to the anode does not prevent the horizontalarrangement. After an action of the current for about twenty minutes theetching is usually sufliciently deep'for lithographic or otherlightly-etched printing-plates, The plate'is then removed from the bathand replaced by a new one. The plate after removal, to which adhere allthe impurities and foreign bodies of ordinary rolled Zinc, is first'Wiped with a soft wet cloth or the like. It is then again treated withzince'tc'hing fluid or acid, which precipitates or dissolvesthe lead inorder to convert the last particles of lead still adhering to it intocolorles's white substance, which will not intersalt which can be was edoff.

square decimeter of the active su In place of a plate a cylinderelectrolyticany provided with a zinc coating of sufiicient thickness canbe subjected to the etching process. In this case the process only needsalteration in that the cylinder which acts as anode is rotated duringthe etchin process.

. e deep etching has the drawback for certain kinds of print, especiallyfor rotary print, that too much water collects and adheres to thehighly-etched drawing, which thus reaches the printing-rolls and causesa gray feeble not sufficiently-pronounced rint. This drawback may beavoided by pl ticing the Zinc plates after previous cleansing in a bathconsisting of a salt solution and subjecting them as anodes to theaction of an electric current until the upper surface layer, whichduring the rolling has received another physical coi'istitution inconsequence of the mechanical pressure thus exercised upon it, has beenremoved. In this manner there is attained, first, that the surface ofthe zinc plate can be more easily scoured and ground, and that,secondly, in the case of dee etching the zinc plate can be etchedshaiiower than without the aforesaid treatment is possible byelectrolysis. In the presence of a superficial layer of differentphysical properties the etching must be continued to a great depth.'lhis process is preferably conducted as follows: The plate of rolledzinc is first cleaned, then brought into the salt solution serving asthe bath and exposed to electrolysis as anode. The cathode is preferablyalso constructed of zinc, and the electrolytic fluid is preferably asolution of a zinc-salt. For the current strength two amperes for eachsquare decimeter of surface is usually sufficient. In the case of a lesscurrent strength the etchin does not proceed quickly enough, whereas tthe increase of the current strength over one ampere usually betterresults are obtained.

After the above-described electrolytic prc aration the zinc plate iswashed, the acid d irectly removed, provided with print, or else againground and further treated.

Having now described our invention and in what manner the same is to beperformed, what .we claim, and desire to secure by Letters Patent, is iI 1. The herein-described electrolytic process of deeply etching zincwhich consists in exposing a zinc plate as an anode to an electriccurrent of at least two am eres per rface while submerged in a bath ofzinc-salt, substantially as described.

2. The herein-described electrolytic process of deeply etching zincwhich consists in providing said zinc, with a print or transfer,sprinkling it with asphaltuln dust and then exposing said zinc plate asan anode to an electric current of at least two amperes per squaredecimeter of the active surface, while submerged in a bath of zinc-salt,substantially as described.

3. The herein-described electrolytic process of deeply etching zincwhich consists in exposing a zinc plate tric current while submerged ina salt solution and removing the surface-layer, washing the plate duringtransferring and then exposing it as an anode to an electric current ofat least two amperes per square decimeter of the active surface whilesubmerged in a bath of zinc-salt, substantially as described.

4. Process for deep etching of zinc by electrolysis for the purpose ofprinting impresas an anode to an elecsi ons therefrom, whiehprocessconsists in 1 In witness whereof we have hereunto set preparmg a zmeeyhnder, and exposmg 1t as ourha'nds 1n presence of two wltnesses.

anode to a current of at least two amperes OTTO CARL STRECKER.

per square decilneter 0f the surface facing HANS HE-RMANN STRECKER. 5the cathode, in a bath of a suitable zine-salt, Witnesses: I

thereby se arating the zinc at the cathode, WALTER HOUSING,

substantia 1y as described. -WALTER SCHUMANN.

